What is...?

In the 1930s, Einstein, Podolsky and Rosen devised the "EPR paradox", which shed light on a peculiar phenomenon in the mathematical modeling of quantum mechanics:  Very far apart particles can exhibit correlated behaviour, which seemed to suggest a faster than light transfer of information between the particles (which in turn would violate assumptions of relativity theory) --- this phenomenon was termed "spooky action at a distance". John Bell (1960s) devised a thought experiment which allows to classically verify whether these correlations actually occur in nature; Aspect, Clauser and Zeilinger received the 2022 Nobel prize in physics, partially for devising and conducting such experiments. In modern terms, these experiments are called "Non-local Games". I will discuss contemporary research related to these non-local games, and in particular some implications of complexity theoretic questions one may ask about them.